The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for moving an actuator assembly within a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The methods for positioning the transducers can generally be grouped into two categories. Disc drives with linear actuators move the transducer linearly generally along a radial line to position the transducers over the various tracks on the information storage disc. Disc drives also have rotary actuators which are mounted to the base of the disc drive for arcuate movement of the transducers across the tracks of the information storage disc. Rotary actuators position transducers by rotationally moving them to a specified location on an information recording disc. A rotary actuator positions the transducer quickly and precisely.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator and is positioned at one end of the actuator. The voice coil is wound upon a bobbin which is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A set of permanent magnets is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A top plate and a bottom plate are generally used to attach the set of permanent magnets of the voice coil motor to the base. The top plate and the bottom plate also direct the flux of the set of permanent magnets. Since the voice coil sandwiched between the set of permanent magnets and top plate and bottom plate which produces a magnetic field, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
One development in the computer industry has been the miniaturization and portability of computers. Currently, there are portable and notebook computers that can be carried in a briefcase or even held in a user""s hand. Since these computers are more likely to be dropped, many computer manufacturers now require that the disc drives used in these computers be shock resistant. The disc drive is one of the components in a computer that is most vulnerable to failure after a shock event. One of the solutions is to use a ramp.
The computer manufacturer""s aggressive, non-operating shock requirements have brought on new methodologies for loading and unloading the read-write heads. One of the solutions to achieving the new shock requirements is to park the heads completely off the discs on a ramp composed of a soft, low friction plastic material. This requires an increase in the overall sweep angle of the actuator assembly. Simply put, the actuator assembly must move through a larger arc in order to park the heads onto a ramp off the disc. To increase the overall sweep angle, the magnet arc length may be increased and the actuator coil may be widened. Essentially, the voice coil motor size is increased to provide for a larger arc length. This solution is costly as a result of the extra magnet, steel, and wire material required. In addition, this solution would degrade the overall performance of the disc drive since the mass limitations on the coil to balance the arm, and the additional wire would reduce access times associated with the voice coil motor.
What is needed is a disc drive which has an actuator assembly having an arc angle which will allow the sliders and attached transducers to be parked or unloaded onto a ramp adjacent the disc drive. What is also needed is a voice coil motor having good performance characteristics which either meet or exceed current performance characteristics. What is further needed is an apparatus that weighs approximately the same or less than current disc drives and which is reliable. There is also a need for an actuator having an increased arc sweep angle with little or no time during which the actuator will not respond to control signals used to move the actuator. Preferably, the actuator should reliably sweep the entire designed arc angle. What is also needed is an actuator motor that allows a portion of the voice coil to pass through the transition zone of the magnets of the voice coil motor without becoming fixed in a single position. A method and apparatus are also needed which can be accommodated using manufacturing techniques close to current manufacturing techniques.
A disc drive includes a base and a voice coil magnet attached to the base. The voice coil magnet has a first portion for providing a magnetic field having a first direction and magnitude, and a second portion for providing a magnetic field having a second direction and magnitude. The voice coil magnet also has a transition zone between the first portion and the second portion of the voice coil magnet where the magnetic field from the first portion substantially cancels the magnetic field from the second portion of the voice coil magnet. The disc drive also includes an actuator assembly rotatably attached to base. The actuator assembly includes a yoke, and a voice coil attached to the yoke of the actuator. The voice coil is positioned within the magnetic field of the voice coil magnet such that passing a current through the voice coil generates a second magnetic field to position the actuator assembly. A ferromagnetic material is attached to the actuator assembly. The ferromagnetic material is positioned within the magnetic field of the voice coil magnet to induce a force from the magnetic field of the voice coil magnet to drive the actuator to a park position. The disc drive may have a ramp attached to the base. Placing the actuator assembly in the park position places a portion of the actuator assembly on the ramp.
The ferromagnetic material is positioned on the actuator assembly to drive the actuator assembly past the transition zone between the first portion and the second portion of the voice coil magnet. The ferromagnetic material may produce a sufficient force to park the actuator assembly on the ramp. The ferromagnetic material may be made of steel and may be in the form of a pin. The ferromagnetic material is attached to the yoke of the actuator assembly. The actuator assembly has an actuator pivot axis. The ferromagnetic material is attached at an end of the yoke farthest away from the pivot axis of the actuator assembly. Preferably, the actuator assembly has a substantially constant velocity as the actuator assembly pivots to a park position. The disc drive further includes a controller for controlling the amount of current passing through the voice coil. The controller reduces the amount of current in the voice coil when a portion of the voice coil is passing near the transition zone. The controller may control the amount of current in the voice coil so that the actuator assembly has a substantially constant velocity as the actuator assembly moves to a park position.
Also disclosed is a method for controlling the movement of an actuator in a disk drive as an actuator assembly unloads a plurality of transducers from a plurality of surfaces of at least one disc. The actuator assembly includes a voice coil attached to a yoke and positioned within a magnetic field. The actuator assembly includes a ferromagnetic material attached to the yoke. The method includes the steps of determining the torque applied to the actuator assembly by the voice coil at various positions as the actuator assembly moves to a park position, and reducing the amount of current in the voice coil as the torque applied to the actuator assembly drops so that a force produced by the ferromagnetic material attached to the yoke acts on the actuator assembly. In another embodiment, the current may be reduced when a leg of a voice coil motor approaches a transition zone in the magnetic field. The method further includes the step of reversing the direction of the current in the voice coil. Reversing the direction of the current in the voice coil produces a force in substantially the same direction as the force produced by the ferromagnetic material attached to the yoke acts on the actuator assembly.
Advantageously, the disc drive which uses the above inventions allows the actuator assembly to swing through an arc angle to allow the sliders and attached transducers to be parked or unloaded onto a ramp adjacent the disc drive. The voice coil motor used has performance characteristics which either meet or exceed the performance characteristics associated with currently used actuator assemblies. The same size coil and the same size magnets are used so the disc drive weighs approximately the same or less than current disc drives. The voice coil motor may be commutated which means that the current in the voice coil is switched at a selected time to produce a force that can be used to move the actuator assembly and attached sliders and transducers to an unloaded position. The ferromagnetic material is placed on the actuator to produce a bias force which induces motion in the actuator arm assembly so that it crosses the magnetic transition zone without getting stuck. The ferromagnetic material can be used with or without commutating the voice coil motor. The resulting voice coil motor is reliable since the actuator moves through the transition zone based on the induced force. As a result, the actuator assembly reliably sweeps the entire designed arc angle. The actuator assembly has an increased arc sweep angle with little or no time during which the actuator will not respond to control signals used to move the actuator. One of the legs of the voice coil can pass through the transition zone of the magnets of the voice coil motor without becoming fixed in a single position. The actuator assembly and magnet assembly undergoes some modifications to implement the invention in addition to potential software changes for controlling the voice coil. Therefore, the method and apparatus can be accommodated using manufacturing techniques close to current manufacturing techniques.